Millions of migrating cows are at risk of death on the Sudan-South Sudan border, nomads said on Thursday, because the frontier has not opened as agreed by the two nations several months ago.
The cattle have fallen victim to the inability of Sudan and South Sudan to implement key security and economic agreements which their presidents signed in September.
The pacts called for a reopening of border points, as part of peace efforts following a March-April war on the undemarcated frontier.
"We want to cross the river with our animals but South Sudan has closed the area," Mahmoud Gibril, a local leader from the nomadic Rezeigat tribe, told AFP.
He said two million cows, their herders and families have been stuck north of the Bahr al-Arab River since mid-December, waiting to go south on their annual migration.
"These cows are suffering from a lack of grass and water," Gibril said.
Late in December, the Rezeigat and "armed groups" from South Sudan clashed around the river at Samaha, according to the Sudanese military.
The area, which Sudan considers part of East Darfur state, is disputed by the two countries.
Gibril said South Sudanese security forces have a compound along the waterway "and they don't allow anyone to come near."
The blockade has concentrated the nomads and their animals in a small area, where there is no Sudanese military or police presence, he added.
"If this continues until the beginning of April most of these animals will die," Gibril said.
A foreign diplomat told AFP that the borders have never been as tightly shut as this year.
"I am worried at the moment about developments on the ground," said the diplomat, asking for anonymity.
Another Rezeigat cattle herder, Idam Abubakr, told AFP that the nomads depend on water from the Bahr al-Arab but South Sudan had "occupied" Samaha which prevented passage.
"Two weeks ago, 90 cows went to the river and were taken by South Sudan's army," Abubakr said.
To avoid clashing with South Sudan the nomads and their animals face a double jeopardy, he said: Either go back north where there is no water, or remain in their current position where they have grass to eat but nothing to drink.
"If they stay in this area until the end of March and the problem is not solved, they will lose their animals," Abubakr said.
The September agreements, along with opening the borders for trade and passage, allowed for a demilitarised buffer zone along the frontier and a resumption of South Sudanese oil exports through northern pipelines.
Khartoum's accusation that South Sudan, which separated in 2011, supports rebels north of the border has been a major obstacle to implementing the deals.